1. Field of the Invention
The present invention relates to a fluid fan clutch of a system in which fan rotation for engine cooling in an automobile or the like is controlled, according to a change in ambient temperature or in the rotation, and in particular to a highly reactive fluid fan coupling device that achieves speeding up of a reaction of fan rotation with the use of a control signal.
2. Description of the Related Art
Conventionally, a fan coupling device that controls fan rotation for engine cooling in an automobile or the like to supply the engine with cooling air is of a temperature-sensitive type, an externally-controlled type, or the like. In an example of the temperature-sensitive type, the inside of a sealed housing composed of a case and a cover is partitioned in an oil reservoir chamber and a torque transmission chamber with a drive disk therein by a partition plate having an oil supply adjusting hole, a dam is formed in a portion of an inner circumferential wall of the sealed housing opposite an outer circumferential wall portion of the drive disk for collecting and reservoiring oil at a rotating time, a circulating flow passage continuing from the dam is formed between the torque transmission chamber and the oil reservoir chamber, and a valve member opening the supply adjusting hole of the partition plate when the external ambient temperature or the like exceeds a set value and closing the supply adjusting hole of the partition plate at equal to or less than the set value is provided inside, and the effective contact area of the oil in a torque transmission clearance provided between the drive disk and an opposite wall face near the outside of the sealed housing is increased/decreased, thereby controlling torque transmission from a drive side to the sealed housing on a driven side. The fan coupling device of this type generally detects an atmospheric temperature using a bimetallic strip or a bimetallic coil, thereby adjusting the opening degree of the oil supply adjusting hole according to this detection value (see Japanese Patent Publication No. S63-21048). In addition, the externally-controlled type has the same basic structure as that of the temperature-sensitive fan coupling device, but in the externally-controlled type, a valve member, which opens and closes the oil supply adjusting hole of the partition plate, is made of a magnetic material, and the valve member with magnetic property is controlled by an electromagnet located outside, and in the valve control structure, for example, a pair of electromagnets are located on a front face side of the sealed housing or on a rear face side thereof, and a valve member with magnetic property which opens and closes the oil supply adjusting hole of the partition plate is located opposite the electromagnets (see Japanese Patent Application Laid-Open No. H03-61727, Japanese Patent Application Laid-Open No. 2002-81466, Japanese Patent Application Laid-Open No. 2003-239741, Japanese Patent Application Laid-Open No. 2004-340373 and Japanese Patent Application Laid-Open No. 2006-112466, etc.).
In the conventional fan coupling devices described above, since such a mechanism is adopted that the drive torque of the drive disk is transmitted to the sealed case by the oil supplied from the oil reservoir chamber to the torque transmission chamber through the oil supply adjusting hole of the partition plate so that the fan attached to the sealed housing is rotated, the oil supply adjusting hole that is opened and closed by the valve member is located on the driven side. Therefore, in the conventional fluid-type fan coupling device of this type, the centrifugal force decreases during low fan rotation (OFF rotation), and the oil supply amount decreases accordingly, so that there is the disadvantage that it takes time to rotate the fan at high speed due to a slow reaction when the fan rotation is to be increased. Furthermore, in a snowplow (a vehicle provided with a blade for snow removal in front of the front grille), the wind speed in front of the front grille becomes lower than the wind speed around the front grille, and a pressure difference occurs between inside the engine room and around the front grille, or a swirling-up wind from the bottom causes a stream of wind in the opposite direction from the fan, thereby reducing the fan rotation significantly, so that there is the disadvantage that the fan rotation does not increase due to a slow reaction or no reaction when the fan rotation is to be increased, resulting in overheating.
The present invention has been made in order to overcome the above disadvantages of the conventional fluid fan coupling devices, and an object thereof is to provide a highly-reactive fluid fan coupling device that utilizes the non-Newtonian fluid characteristics of oil to obtain an excellent reaction rate of fan rotation with the use of a control signal.